The invention relates to a recombinant DNA coding for a novel protein having .beta.-1,3-glucanase activity, or for a precursor of this protein, to a bacterium containing this recombinant DNA, to a plant cell, plant or plant part, especially a plant seed, transformed by this recombinant DNA, as well as to this novel protein and to a method for preparing it.
Crop plants are known to be subjected to attack by-parasites such as phytopathogenic fungi, which are responsible for substantial harvest losses. The .main means at present for controlling these fungi lies in the use of chemical substances having fungicidal activity. It is now known that plants react naturally to such attack by various defence mechanisms, which are unfortunately, in general, triggered too late and at too low an intensity to be sufficiently effective.
One of these mechanisms comprises the induction of an enzyme known as .beta.-1,3-glucanase E.C.3.2.1.39 (Kombrink et al., 1988, Pr. Ntl. Acad. Sci. USA, 85,982-986 and Pegg et al., 1981, Physiol. Plant. Pathol. 19,371-382). This induction can be triggered artificially through the effect of elicitors, that is to say compounds of biological origin capable of inducing in a healthy plant the defence reactions which it deploys naturally during an infection by pathogenic agents, or during a hormonal imbalance caused by auxin, cytokinins or ethylene (Abeles et al., 1971, Plant Physiol. 47,129-134 and de Loose et al., 1988, Gene, 70,13-23).
.beta.-1,3-glucans are linear polysaccharide polymers consisting of glucose units linked via .beta.-(1.fwdarw.3) linkages, sometimes possessing .beta.-(1.fwdarw.4) or .beta.-(1.fwdarw.6) type branching (Farka 1982, in "Fungal protoplasts", Peberdy and Ferencry, published by Dekker Inc.). These polysaccharides constitute a typical component of the skeleton of the wall of most fungi, and in particular phytopathogenic fungi. .beta.-1,3-glucanases are capable of degrading them by fragmentation of the .beta.-1,3-glucan chains. Most known plant .beta.-1,3-glucanases are of the endo type.
It is known, moreover, that recent progress in so-called recombinant DNA technology and in the transformation of plant cells, as well as in the regeneration of whole plants from the latter, enable a gene of interest to be introduced into plant cells, a plant or a plant part so as to obtain an advantageous phenotype.